Turbomachine rotor

ABSTRACT

A turbine rotor assembly comprising a cast hub and a series of integral airfoil blades extending radially outward from its rim. A series of holes and thin slots extend through the hub in between adjacent blades to minimize stress caused by differential thermal expansion and to place the natural frequency of the blades outside the normal operating range of the rotor. End caps and tubular inserts are received in the holes and held in place by deforming the inserts into circumferential grooves.

United, States Patent 11 1 Straniti Nov. 12, 1974 TURBOMACHINE ROTOR FOREIGN PATENTS OR APPLICATIONS 1751 lnvemori Salvatore Stranifi, Orange, Com 609.446 9/1948 ore-61 13min 4l6/244 A [73] Assignee: Avco CorporatiomStratford, Conn. P E E A P H J rimarv xaminerverette owe r. [.22] F'led: Attorney, Agent, or Firm-Charles M. Hogan; lrwin P. [2]] Appl. No.: 420,204 Garfinkle 52 us. 01. 416/244 [57] ABSTRACT v [51] Int. Cl......' .f. F0 l d 5(08 A turbine rotor assembly comprising a cast hub and a [58] Field Of Search 416/244 A, 221 series of integral airfoil blades extending radially utward from its rim. A series of holes and thin slots ex- [56] References Cited tend through the hub in between adjacent blades to UNITED STATES PATENTS minimize stress caused by differential thermal expan- 737,042 8/1903 Stumpf 416 244 A and to Place the natural frequemy of the blades 2,753,149 7/l956 Kurti 416 221 ux Outside the normal Operating range of the FOIOF- End 2,953,348 9/1960 Leland 416/221 p and tubular inserts are received in the holes and 3,255,994 6/1966 Dreimimis 416/244 A held in place by deforming the inserts into circumfer- 3,262,676 7/1966 Huebner et al. 416/244 A ential grooves. 3,291,446 l2/l966 Huebner 4l6/244 A X 3 2 5 3 1/1967 2 Claims, 4 Drawing Figures Nickles 416/221 PATENIEUHBVIZ i974 I 3; L sum 10? 2 847 506 TURBOMACHINE RoToR The present invention relates to turbomachine rotors and more specifically to simplified rotors of this type.

One of the biggest obstacles to the mass production of a truly economical gas turbine engine has been the rotor construction. Present day turbomachine rotor assemblies generally comprise a machined or forged hub having a series of axial dovetailed slots around its periphery. Individual blades, generally cast, have root sections received in the dovetailed grooves. Suitable retaining devices lock the blades axially to make up a completed rotor assembly. Although these rotors are quite effective from an aerodynamic and thermodynamic standpoint, they are extremely difficult to manufacture. The reason for this is that the unit has a larger number of individual-pieces that must be made to particular tolerances to permit final assembly. In addition, they must be assembled by hand using timeconsuming and expensive methods.

The above problems are solved in accordance with the present invention by a turbomachine rotor comprising a central annular hub and a plurality of integral airfoil blades. The blades extend outward from the rim of the hub at spaced circumferential positions around its periphery. The annular hub had cutaway portions adjacent its rim for minimizing stresses caused by differential thermal expansion and for minimizing vibratory stresses.

The above and other related features of the present invention will be apparent from a reading of the following description of the disclosure shown in the accompanying drawings and the novelty thereof pointed out in the appended claims.

In the drawings:

FIG. l is a simplified longitudinal section view of a gas turbine engine incorporating a turbomachine rotor which embodies the present invention;

FIG. 2 is a greatly enlarged fragmentary section view of the turbomachine rotor shown in FIG. 1;

FIG. 3 is an end view of the turbomachine rotor of FIG. 2, taken on line 3-3 of FIG. 2; and

FIG. 4 is a plan view of the turbomachine rotor of FIG. 2, taken on line 4-4 of FIG. 2.

FIG. 1 illustrates a gas turbine'engine comprising an output gearbox which supports an annular compressor'inlet housing 12. Air passes inward through an annular compressor inlet passage 14 formed in housing 12 into a compressor 16 comprising an axial flow bladed hub 18, a fixed axial flow stator 20, and a centrifugal impeller 22. Hub l8 and impeller 22 are mounted on a shaft 24 journaled at its forward end by bearing assembly 26 received in housing 12. Air is discharged from the periphery of impeller 22 into a diffuser 28 which has expanding passages for increasing the static pressure of the air.

From these the pressurized air passes through a turning vane assembly 30 and into a chamber 32 formed by an annular outer housing 34 and an inner cast strut assembly 36. A perforated annular combustor 38 is positioned in chamber 32 and has a plurality of nozzles 40 (only one is shown) which inject metered fuel into combustor 38 for mixing with pressurized air passing inward through the perforations. A suitable device ignites the fuel/air mixture to produce a hot gas stream.

The hot gas stream passes through a turbine inlet duct 42 and from a turbine inlet nozzle 44.

The hot gas stream then passes across a bladed turbine rotor 46, to be described in detail later. Turbine rotor 46 is also mounted on shaft 24 and spaced from centrifugal hub 22 by a conical element 48. A bearing assembly 50 adjacent rotor 46 journals the aft end of shaft 24 for rotation. After the hot gas stream leaves the turbine rotor 46 it passes across a bladed power turbine hub 52 which is journaled in strut assembly 36 by a bearing 54. Hub 52 has an integral output shaft 56 extending forward to a speed-reduction gearset (not shown) in output gearbox l0. 7

In accordance with the present invention turbine rotor 46 is designed in such a way that it is extremely simple and economical to manufacture. Referring particularly to FIGS. 2, 3 and 4, turbine rotor 46 comprises an annular hub 60 having a rim 62 and a central opening 64 telescoped over shaft 24 (see FIG. 1). A plurality of airfoil-shaped blades 66 are integral with hub 60 and project radially outwardly from rim 62 of hub 60. Hub 60 and blades 66 are preferably cast from a hightemperature alloy normally used to form cast turbine blades. Thesetypes of alloys are strong enough to be used for the hub 60 and withstand centrifugal forces during rotation. Blades 66 have a root section stagger angle a which defines an acute angle relative to the axis A of the hub 60. Hub 60 has a plurality of holes 68 extending from its forward face 70 to its aft face 72 adjacent its rim 62. As is particularly evident in FIG. 4, the holes 68 are positioned in between adjacent blades 66 and have their axis generally parallel to the line S defining the stagger angle a. In addition, as seen in FIG. 2, the upstream ends of the holes 68 are radially outward relative to the downstream ends. Each hole 68 has a slot 74 extending radially outward from the hole 68 to the rim 62 of hub 60. As described below, slot 74 is ex tremely thin and it is conveniently formed by EDM or other suitable production technique. Each hole 68 has an annular shoulder '76 formed at its upstream end and a circumferential groove 78 formed at its downstream end. A cup 80 is received in each hole 68 and is maintained against shoulder 76 by a tubular element 82. Tubular element 82 is deformed radially outward at 84 to hold the assembly in each hole 68.

When the engine is in operation the hot gas stream passing across blades 66 and rim 62 causes a very large temperature gradient relative to the inner sections of hub 60. The holes 68 and slots 74 permit the rim section of the hub 60 to freely expandin response to the high temperature without creating undue stresses.

The series of holes and slots also define sections 86 in between adjacent holes that act to in effect elongate the blades and permit them to flex. The position of the holes 68 relative to the rim 62 can be varied to achieve blades with predetermined natural frequencies of vibration. This frequency is selected so that it will lie outside of the normal operating range for the engine. When vibrating conditions are encountered the walls of slots 74 frictionally engage one another to damp the vibrations. Also, the tube 82 is forced against the radially outward walls of holes 68 by centrifugal force to damp vibration.

The cup 80 prevents the passage of fluid through holes 68 to maintain high efficiency. While some flow could be expected across slot 74, it is so small in width (approximately .003 to .007 inches) that the leakage through this slot is negligible. Although the pressure differential acts to push the cup 80 and tube 82 out of holes 68, centrifugal force urges them toward the upstream end of the holes. ln addition, the flared-out section 84 adequately holds the tube 82 in place.

The above turbomachine rotor is extremely simplified and is capable of being manufactured using lowcost, high-volume production techniques. At the same time, however, it enables the high level of thermodynamic efficiency and minimizes problems associated with differential thermal expansion and vibratory effects.

While a preferred embodiment of the present invention has been described, it should be apparent to those skilled in the art that it may be practiced in other forms without departing from its spirit and scope.

Having thus described the invention what is claimed as novel and desired to be secured by Letters Patent of the United States is:

l. A one-piece cast turbomachine rotor comprising:

a central cylindrical hub;

a plurality of airfoil blades integral with and extending outward from the periphery of said hub at spaced circumferential positions around the rim of said hub, said blades having an acute stagger angle relative to the axis of said hub;

a plurality of holes in said annular hub, said holes extending generally parallel to the stagger angle line of said blades, said holes each having an annular shoulder of reduced diameter formed adjacent one end thereof, and an annular recess of enlarged diameter adjacent the opposite end thereof;

a like plurality of continuous slots, each of said slots extending radially outward from a respective hole and through the rim of said hub, said slots also extending in a line parallel to said stagger angle line; and

a generally cylindrical cup compressed into each of said holes, said cup being closed at one end and having a configuration complementary to said holes whereby said cups are retained in said holes between said shoulders and said recesses.

2. A turbomachine rotor as in claim 1 wherein said holes are positioned at a predetermined location relative to the periphery of said hub thereby producing a given natural frequency of vibration for said blades whereby said rotor may be tuned to a frequency lying outside its normal operating range. =2: 4: 

1. A one-piece cast turbomachine rotor comprising: a central cylindrical hub; a plurality of airfoil blades integral with and extending outward from the periphery of said hub at spaced circumferential positions around the rim of said hub, said blades having an acute stagger angle relative to the axis of said hub; a plurality of holes in said annular hub, said holes extending generally parallel to the stagger angle line of said blades, said holes each having an annular shoulder of reduced diameter formed adjacent one end thereof, and an annular recess of enlarged diameter adjacent the opposite end thereof; a like plurality of continuous slots, each of said slots extending radially outward from a respective hole and through the rim of said hub, said slots also extending in a line parallel to said stagger angle line; and a generally cylindrical cup compressed into each of said holes, said cup being closed at one end and having a configuration complementary to said holes whereby said cups are retained in said holes between said shoulders and said recesses.
 2. A turbomachine rotor as in claim 1 wherein said holes are positioned at a predetermined location relative to the periphery of said hub thereby producing a given natural frequency of vibration for said blades whereby said rotor may be tuned to a frequency lying outside its normal operating range. 